While the exact location of your breasts does not directly cause back pain, sagging breasts do have a high correlation with back and shoulder pain. Wearing a non-supportive bra, poor posture and weak back muscles cause the breasts to appear more saggy and contribute to pain in the back. Fortunately, many remedies for both conditions can bring relief.
In many cases, sagging breasts are caused by an ineffective bra. A poorly fitting bra -- or wearing no bra at all -- can cause pain in the upper back and shoulders. When the breasts aren't supported, the weight tends to draw the shoulders forward, causing the back to hunch and forcing the upper and mid back to strain. According to a study by the University Hospital of Wales, pre-menopausal women who go without a bra for a period of three months tend to have 7 percent more back pain than women who wear effective bras regularly.
Sagging breasts are also exacerbated by poor posture. If you have good posture, your vertebrae are stacked on top of each other -- and the shoulder blades are engaged and drawn together -- lifting the breasts forward and up. If you have bad posture, particularly in your upper back, not only do your breasts tend to drop, you are also causing pain in your shoulders and upper back because hunching forward creates strain in the muscles that run along the spine.
Your breasts might also appear lower if your back and pectorals are not strong enough to support the weight of your breasts. Without strong rhomboids which are the muscles between the shoulder blades, latisimus dorsi, the muscles that form the "V" shape in the back, and pectorals which are the muscles in the back, your breasts can cause muscular and skeletal pain. Strengthening exercises will help the muscles support the weight of the breast and keep the skeletal system in line.